A variety of structures including buildings and ships have been placed in the ocean for development of natural resources such as biological, oil, gas and mineral resources, for exploitation of ocean energy, ocean space, seawater, etc, for preservation of environment, etc, or for industrial applications for marine transport, harbor, marine product industry, etc.
In such structures, steel materials are generally employed, although materials are selected considering their purposes, costs, strength, durability, etc.
However, when these structures are placed in seawater, the surface of the structure in contact with seawater becomes a suitable environment for reproduction of marine organisms, and the marine organisms may cling to and thus damage the surface of the structure. On the other hand, since seawater provides a severe corrosion environment to the steel materials, corrosion will grow with time, resulting in deterioration of the structure.
In order to solve such a problem, adequate coating has been performed on the surface of the structure, with periodical repainting.
However, repainting requires removal of old paint, which takes a lot of time and labor, posing a problem of marine pollution due to stripped paint flakes. Also, clinging marine organisms should be removed for repainting, in which case it must be ensured that the removed dead organisms never sink to the bottom of the sea to be decomposed. Such a work must be very difficult.
On the other hand, coating materials have been developed preventing corrosion due to oxidation of the surface of the structure. Although such materials have effects of retarding growth of the corrosion, however, they contain zinc, lead, cupper, etc, raising a problem of environmental pollution due to dissolution of these metals into seawater. In addition, none of these coating materials can prevent clinging of marine organisms, and if they cling to the structure, oxidation is accelerated by oxygen sent out from the marine organisms, causing further growth of the corrosion of the structure.
Alternatively, an idea has been suggested in which a vibration may be applied to the structure. It is reported that vibrating a structure prevents clinging of fungi or algae. However, it has not been clear what type of vibration should be applied and how. In addition, even if no marine organisms cling to the structure, seawater causes rust, resulting in corrosion of the structure.
In view of the foregoing, it is the object of this invention to provide a method of preventing deterioration of a submerged marine structure, capable of preventing clinging of marine organisms and corrosion due to rust, and capable of effecting long life of the structure, and a suitable ultrasonic vibration unit for use in the method.